How to rescue a sunflower wild relative

A paper by Jennifer R. Ellis and David E. McCauley of Vanderbilt University, just out in Biological Conservation, tries to answer a couple of quite controversial questions for conservationists: ((Ellis, J., & McCauley, D. (2009). Phenotypic differentiation in fitness related traits between populations of an extremely rare sunflower: Conservation management of isolated populations. Biological Conservation. DOI: 10.1016/j.biocon.2009.03.029)) How do you prioritize populations for conservation? And when does genetic pollution become genetic rescue? Both answers depend on something most gene-jockeys don’t do much of: growing plants and seeing how they perform.

To add piquancy, the paper deals with a crop wild relative, and a very rare one at that: Helianthus verticillatus, which is known from only four sites in the southeastern United States. The authors worked on populations from two of these, in Tennessee (fewer than 100 individuals) and Alabama (several hundred individuals). They collected seeds from sixteen of what they had previously identified as genetically distinct individuals from each population, and then made a whole bunch of crosses, both within populations and also between the two populations, for two generations. They grew the progeny of these crosses in the same environment and measured how well they did in terms of fruit viability, germination, survival and pollen quality.

So, first, to the prioritization question. Genetic markers are now routinely used to identify populations that are particularly low in diversity and thus in need of immediate in situ protection or collecting for ex situ conservation. Often, genetic diversity is positively correlated with fitness, but this is not always the case. For H. verticillatus, in fact, it was known from previous marker studies that the two populations had comparable levels of genetic diversity and only moderate genetic differentiation. However, the results of the common environment study on the offspring of the intra-population crosses showed that they different significantly in their overall “fitness,” with the Tennessee material having lower germination rates and fruit viability. In other words, molecular markers on their own would not have raised a particular concern about the long-term viability of the Tennessee population. In the words of the authors, “contrary to genetic marker information, these populations are not interchangeable with regard to quantitative fitness characters.”

Next, the genetic rescue question. The conventional wisdom of course is that conservation should strive to maintain the genetic integrity of populations. Bringing in material from elsewhere constitutes genetic pollution and is BAD. The introduction of new genetic material into relatively homogeneous populations with low fitness can of course result in heterosis and increased fitness. But it can also lead to lower fitness — inoutbreeding depression — “owing to the dilution of local adaptations or disruption of co-adapted gene combinations.” Enter the inter-population crosses. Crossing Tennessee individuals with those from Alabama resulted in offspring that were more fit, with no sign of outbreeding depression, at least for the two generations of the study. This “offers great promise” as an active conservation strategy for the Tennessee population, the authors say.

Given people’s sqeamishness about messing around with rare species, I wonder if such activism will be given a chance.

Nibbles: Sheep, Yams, Satellites, Payment for ecosystem services, Museum

Cattle domestication

I was going to write about some recent papers on the domestication of cattle myself, but things got a bit hectic and I didn’t find time. I did, however, find Razib’s post at Gene Expression, and I commend it to you. Of course there’s a lot in there about the genes for milk production, and some worrying nonsense about using genome information to breed better cattle or, to put it another way “accelerating livestock genetic improvement for milk and meat production”. Breeders making use of super-sires and super-ovulating cows have already done a pretty good job of reducing the diversity of extant cattle, and I for one am not convinced by the need for ever more efficient use-once-then-dispose-of milk machines. But I haven’t read the papers, so I can’t comment further. I am intrigued, however, by this statement, quoted by Razib:

Domestication and artificial selection appear to have left detectable signatures of selection within the cattle genome, yet the current levels of diversity within breeds are at least as great as exists within humans.

If we’re not suffering from having passed through genetic narrows, maybe cattle aren’t either. Maybe they’re just suffering.

Nibbles: Japan, Bananas, GMO, Bees, Squirrels, Mangroves, Climate change and indigenous people, Goji, Svalbard, Heirloom rice, Dataporn

How C4 came to be understood

Yesterday was Ada Lovelace day, when bloggers around the world celebrated women in technology. We weren’t aware of it, and frankly, I’m not sure who we might have chosen. Erna Bennett? Fortunately, though, we can direct you instead to Oliver Morton’s fine post on Constance Hartt. Who she?

Hartt was a laboratory researcher at the Hawaiian Sugar Planters Association Experiment Station, and her assiduous work on the biochemistry of sugar cane in the 1930s and 1940s convinced her that, for that plant at least, the primary product of photosynthesis is malate, a four carbon sugar. Later carbon-14 studies showed that she was right — and led to an interesting conundrum. Why did some plants — most plants, indeed, and almost all algae — make a three carbon sugar, phophoglycerate, while sugar cane and, it later became clear, various other grasses made a four-carbon sugar?

Some gene-jockeys seem to think that all that’s needed to double the yield of crop plants is “simply” to give them a C4 photosynthetic pathway. I’m not going to get into that one. But Morton gives a good account of how and why C4 differs from C3, and the part Hartt played in its elucidation.